To conserve soldiers' lives and provide Army units with operational and tactical advantages, The Department of Defense and The Army work on the development of Mobile Robots and Unmanned Ground Vehicles (UGV) under the Future Combat Systems (FCS) program. Tactical behaviors are essential in order to enable the UGV to perform in a battlefield environment. Most of these behaviors are identified in fighting manuals, standard operating procedures, etc.
A UGV is a member of a maneuvering unit, and it moves in an appropriate position at a particular distance and with a specific mission. Upon receiving information about friendly or enemy situations, tactical maneuvers may use folds in terrain and thick vegetation for cover and concealment, gaining and maintaining contact with an enemy entity without being detected, and occupying a position that provide an optimal line of sight for engaging the enemy. The UGV must be able to report enemy contact and chemical alerts, request orders and support fires. For an armed UGV, tactical behaviors include targeting, engaging, and assessing damage. Targeting includes finding, identifying, and handing off targets. Survivability includes changing battle positions, hiding, firing, and calling for additional support. If captured, a UGV might call in artillery on itself or self-destruct. The UGV must also protect itself from natural dangers and be able to estimate obstacles.
Tactical behaviors for robots have not fully matured yet. Most development efforts are focused on self-preservation. Much work has begun in the area of cognitive modeling, neural networks, Bayesian networks, case-based reasoning, and other decision-making methods. Advances in software for real-time cognitive processes are not being integrated yet into tactical behavior technologies for UGV systems.
Unstructured roads pose a challenge because the roads are likely to appear unmarked, and edges may not be distinct. Current approaches may lose the road on sharp curves or classify steep slopes as obstacles. Obstacle detection on unstructured roads may be more difficult because curves or dips may limit opportunity to look far ahead. Difficulty will be encountered when the “road” is defined more by texture and context. In a combat environment obstacles may include bomb craters, masonry piles, or other debris. On-road mobility in an urban environment is very difficult. In addition, perception performance will be affected by weather, levels of illumination, and natural and manmade obscurants that affect visibility.
There has been significant progress in road following, obstacle detection and avoidance, terrain classification, and traversability analysis for off-road mobility. But despite impressive demonstrations, today's automated systems remain below human driving performance under realistic driving conditions even on structured roads. And there are significant gaps in road-following capability and performance in the urban environment, on unstructured roads and under all-weather conditions.
The nature of combat situations requires FCS to be equipped with a target recognition system. For many years, the solution of target recognition problems was linked to the solution of more generic Pattern Recognition Problem. The successes of pattern recognition algorithms created a hope that they can be used for recognizing targets. But their performance always sharply degraded under field conditions.
Major points of failure of the target recognition system were its inability to separate a target from a clutter, to identify possible target location in a natural environment, and reliably recognize occluded targets. It became apparent soon that reliable target detection and identification go far beyond the scope of the Pattern Recognition Problem.
More importantly, the system was able to react only when something already started happening and target became clearly noticeable, which might not be acceptable for combat situations, especially for FCS. Target may pose a threat, and this threat should be identified and destroyed or avoided before it is too late. Because of that, human observers can monitor and scan potential threat areas and find hidden objects while the modern computer vision systems lack these capabilities.
The real problems of machine perception are not in the imprecision of sensors. In fact, sensors become more and more sophisticated and precise, and they can see far beyond the human senses. But nothing yet can replace human vision in its unique ability to understand and interpret perceptual information. None of the systems can match the performance of an alert human driver, which is using context and experience in addition to perception.
In the human vision, the scene context plays a significant role in the identification of an object.
In many cases such identification is only possible when using context: temporal and spatial relations between the parts of a scene and inferred facts, unobservable in the scene.
In many cases, an object can only be recognized correctly after identification of its role/position in the visual scene. Therefore, the separation of an object from clutter might simply not be feasible without this step.
However, the mainstream of figure-ground separation algorithms still treats image information as a 2-Dimensional array of pixels, and uses simple separation criteria with a bottom-up approach. This usually creates an ambiguity and imprecision, while the natural vision provides unambiguous separation of an object from its background.
It was found that vision and knowledge areas in the brain are linked with forward and back projections, and knowledge is heavily used for object detection and identification. Vision mechanisms can never be completely understood apart from the informational processes related to knowledge and intelligence. Failure of modern computer vision systems is, in a major sense, failure of their knowledge components.
The problem of discrimination of a target from clutter is different from the segmentation of 2-Dimensional array upon some threshold criteria. The unambiguous separation requires the integration of bottom-up fusion of multiple local and regional features with intelligent top-down processes that involve knowledge and context.
There were significant efforts in conversion image data into meaningful informational structures, and also on usage of context in processing of visual information. For instance, Geographic Information Systems (GIS) can effectively address problems with geographic and satellite imagery, because geographic knowledge has been well formalized in the form of maps, and maps can be represented well in computerized form.
In the field of multimedia, the MPEG-7 standard was a wide industry effort to address these problems for generic images, converting them into XML structures. MPEG-7 provides a set of image primitives called Descriptors. The MPEG-7 Description Scheme is the structure and semantics of the relationships between image components, which may be both Descriptors and Description Schemes. A MPEG-7 image description consists of a Description Scheme and a set of Descriptor Values.
MPEG-7 supports a range of abstraction levels, from low-level video features, such as are object's shape, size, texture, color, movement, and position, to high-level semantic information. However, the MPEG-7 standard reflects the present state of image/video processing, and it only provides a set of predefined descriptors and schemas. MPEG-7 Visual Descriptors evolve from low-level image processing, which is well understood and formalized. However, Description Schemas relate to mid- and high-level image processing, which has not yet been well formalized.
Neither automatic and semiautomatic feature extraction nor schema creating algorithms is inside the scope of the MPEG-7 standard. Although most low-level features can be extracted automatically, high-level features and schemas usually need human supervision and annotation. Only the description format in MPEG-7 is fixed and not the extraction and transformation methodologies. These are the areas that must be addressed.
The highest level of image description is the semantic one, and MPEG-7 standardizes information on these levels. But the problem of transforming primary image structures directly into semantic description has not been solved yet, as processes on the intermediary levels are not well understood and formalized.
Although RDF (Resource Description Framework) is better than other schemas in its ability to specify relationships and graphs, the MPEG-7 Group has made a decision to use an easily understandable and readable XML (Extensible Markup Language) Schema Language as the MPEG-7 DDL. However, neither RDF nor XML Schema has been designed to describe complex dynamic hierarchical structures that constitute most of real images.
MPEG-7 Visual Descriptors can be used for searching and filtering images and videos based on several visual features such as color, texture, object shape, object motion, and camera motion. This allows measuring the similarity between images and videos. Such a set of descriptors might be effective for the entire image.
There are other similar approaches toward converting images into their structured description that is based on image low level features and their combinations, which use either top-down or bottom-up flow of processing image data or both types of flow, and attaching linguistic values for semantic querying. The most of arts are trying to convert image into a sort of structural description that can be compared against a similarly described collection of images stored in a database.
These approaches might work well for image and multimedia databases as they allow for creating structured collections of images, and querying them on certain similarity criteria, but not for the robots and UGVs that must perform in the real-time and in hostile environments. These approaches not only add extra steps, but also increase reaction time which might be vital for the real-time systems. More importantly, they are not able to provide the needed level of understanding of the environment by a robot or an Unmanned Ground Vehicle.
Any real world environment has the dynamic nature, and so is visual information. Ambiguity and uncertainty in the real-world visual information can not be resolved without a system of active vision. There are many situations when generation of a meaningful structural description might not be possible for certain image components without interaction with motor programs.
In the brain, spatial perceptual information hierarchically converts from quantities to qualities, from qualities to objects, from objects to spatial situations. Temporal perceptual information converts from changes to actions, from actions and objects to events, from events to “cause and effect” links, and from them to algorithms and scenarios. Feedback projections exist in the brain on every level. They provide context and help to resolve ambiguity and uncertainty.
Such conversions are achieved with the help of mid-level vision. Phenomena of mid-level vision are known as perceptual grouping and organization. They can be partially described with so-called gestalt laws. However, these processes are neither well understood nor formalized. There is no common opinion on how these processes might be represented for computer simulation. As of today, there is a significant gap between low-level image processing and its semantic description.
To be useful in the battlefield component of the Armed Forces, military robots must exhibit predictive situation awareness. This requires a decision support context, and this is not possible without an effective knowledge system that provides effective World Modeling. This is the basis for planning in a generation of behaviors and the resolution of uncertainty in sensory processing. These ideas have been built into the RCS architecture. However, the success or failure of an implementation strongly depends on how effectively different subsystems can communicate with each other and on how effectively knowledge representation serves the goals of the subsystems.
The NIST 4D/RCS architecture provides analysis, design, and implementation methodology for development of real-time control systems using sensory information to guide the intelligent vehicle in the execution of complex tasks. A strong side of RCS architecture is a hierarchical framework for task execution planning and adaptation to changes in the environment.
The traditional approach to tactical-level reasoning is the rule-based systems, implemented either as monolithic decision-trees or finite state machines. Such approaches are inspired by defensive driving literature, where knowledge is often expressed in the form of high-level rules. Simple versions of such rules can be used as a starting point for a rule-based tactical driving system.
The development of intelligent ground vehicles requires a thorough understanding of intelligent behavior, which a UGV must exhibit. Knowledge representation techniques are needed to capture information that the sensor system perceives and organize that knowledge in a fashion that makes it easy to retrieve and process.
Knowledge models exist today in the forms of frames, expert and production systems, logical and functional programs, and DAML and OWL ontologies, etc. Knowledge is captured in the software development area in the form of objects and simulation models, including AI games. The latest wave of knowledge models is built upon the XML trees. Each of the current knowledge models can address certain problems, but not cover everything. J. F. Sowa called this situation “knowledge soup”.
Knowledge systems have been intensively studied beginning in the late 1960s, but the status of knowledge models is very similar to Computer Vision, where numerous theoretical and computational methods exist but none of them can cover the entire process. In the same way, the established methods of knowledge representation capture certain aspects of knowledge processes and models, but none of them can meet the requirements to knowledge representation from the previous page in the first section.
Existing knowledge models are based on artificial theories that are based upon symbolic strings and constructs of a written language. Formal logic has been developed further into a separate branch of science as abstractions of these methods.
The artificial symbolic strings of a written human language cannot serve as a good representation for knowledge models. Written language is just a static reflection of knowledge models and processes, happening in the brain. To obtain a full-scale knowledge system, written language must be accompanied with a context system and with a processor—an inference engine. Although strings of symbols are perfectly readable by humans, it is difficult to build an inference engine for such a representation of knowledge. Such a knowledge system is limited mostly to what a human can type in.
It is well known that expert systems in the late 80's and early 90's have proved themselves to be ineffective in most areas of potential application. Even when it was possible to collect enough knowledge to cover a major number of possible cases of system behavior, there always were some unplanned situations. Because this type of system can handle only situations that have been anticipated and entered into the system via facts and rules, a human being must be involved in the system all the time in the event that an unplanned situation arrives. However, a human operator inside the loop jeopardizes the whole idea of such a system. This representation is good for knowledge acquisition, serving as a mediator between human experts and computers. But it does not serve well for modeling.
In other words, an appearance of knowledge models rather than their true modeling nature was the subject of studies in past. And this approach hid the true modeling capabilities of knowledge systems from researchers and developers.
String representations have no connection to neuroscience and brain research. Without an appropriate theory of knowledge, there was a strong tendency to substitute models of informational processes for models of physical processes in the neural “hardware”. But such models don't appear to capture the essence of informational processes in biological systems. Physical processes are not identical to informational processes. A complex pattern of energy activity in the semiconductors of a microchip is described as a complex set of partial differential equations. But on the informational level it represents Boolean 0-s and 1-s. If differential equations were used instead of Boolean logic, digital computers would remain a highly theoretical idea. For our goals, instead of emulating physical processes in the cortex, it would be better to discover the informational representation of intelligent operations in the cortex.
The unsolved problems with knowledge and lack of its unified representation and processing leave the current arts at the level of separate methods which do not allow them for the creating of a full-scale perception system for robots and unmanned vehicles without meeting additional requirements.
If we look at the commonalities among all known knowledge models, we can find that knowledge has a hierarchical relational nature, and knowledge models can be expressed in the form of graphs and diagrams. The first systems of writing were based on pictorial representation rather than on symbolic strings and they look like pictorial diagrams that show the story in space and time. Diagrams inspired scientists and philosophers such as Charles Sanders Pears to create abstract logical systems. After recognizing the failure of expert systems, there was an intensive search of more natural ways of representing knowledge.
A string is a chain of symbols, whereas a chain is a flat and one-dimensional graph. A chain represents a linear sequence but not a relational model. Moving knowledge representation from strings into a multidimensional graph- or diagrammatic form aids in solving problems that string representation alone suffered from.
This situation begin changing in recent years with the development of multi-agent systems, methods of computational intelligence, and theories of visual languages, graph- and diagram-based representations and other natural representations of knowledge.
In the mainstream of modern software development, World Modeling is supposed to be achieved with a Multi-Agent System, which is connected to a Knowledge Base. An agent represents a model or a process that is supposed to solve certain tasks. The term “Multi-Agent systems” covers multiple sets of agents that are supposed to communicate with each other for solving more complex problems than a single agent can solve.
Today, such systems are built on empirical bases. There is still no widely accepted theory of how knowledge and intelligence can be represented in the brain and how such system works with vision, and what is required for the implementation of an effective knowledge system for perception, prediction, decision making, and control.
Any World Model can be described as a System. A System has an identifiable hierarchical relational structure. However, it is impossible to have a complete set of models for every possible situation. Knowledge is incomplete in this sense. Instead, it helps to build models on the fly from smaller, but verified models.
Knowledge Models include facts and rules. Facts are small fragmentary models of the World that are believed to be true. Rules are generalized fragmentary models, where concrete entities are replaced with classes or roles. When such models come together in an active space, they tend to create a larger model.
Therefore, Knowledge Representation should allow for synthesis, analysis and verification of models, and requires a processor that can handle these operations. These processes are logical. Synthesis is successful if analysis and verification cannot find any contradiction in the created model.
Processes in a robotic system are largely driven by input from the perceptual system, helping to choose the right models. However, perceptual system must speak a language that the knowledge system understands. In other words, perception should have the same representation of models and processes at a certain level that knowledge systems have.
There are relations between the model's components and processes. Other types of relations group entities and processes into sets and classes. These relations can be used for traversing knowledge bases in search of needed fragments and for creating analogies, which are special kinds of rules. Therefore, effective Knowledge Representation requires a context system and must be based on relations. Relations specify constraints in the system.
An important question is how to express components, processes and relations: implicitly or explicitly? From a design point of view this means: what should be hard-coded, and what can be represented with flexible replaceable models.
If we have an implicit representation of relations, they are hardcoded into the designed system. In this case, the system will have a predetermined structure, and can handle a predefined set of cases only. Therefore, in order to allow for changing the structure of the system on the fly, relations in such a system should be represented explicitly with a sort of a special class that represents a relation. A class that represents a model can have a flexible set of “relations” in its properties, and this will allow for changing the structure of the model dynamically.
On the other hand, if we code entities in our system explicitly, then we also have an inflexible model structure where every block is hard-coded. To avoid this, we need an implicit representation for entities via a class that reference such an entity, or points to it. In this case, the structure of the system can also be modified by changing a reference or re-pointing to another entity.
In such a statement of the problem, a system explicitly reveals its structure while using implicit symbolic names for its entities and components. It allows for the incorporation of structural transformations into the runtime system. This makes Knowledge Models dynamic and flexible, and permits their creation and modification dynamically.
There was a gap between the higher-level knowledge representation in the symbolic form and low-level quantitative image information. The mechanism of transfer of quantities into qualities and symbols was not clear for decades and became apparent only recently after many years of development of fuzzy set theory by L. Zadeh and others.
Lack of a unifying representation of knowledge has led to hybrid vision systems combining heuristics and dissimilar approaches. There are a few custom Image Understanding systems, and CAD-based, Model-based, Context-based, Object-based vision systems. They are based on the ideas of recognition as comparison of a primary view of an object with its 3-D model. Such “recognition” can work well only for non-occluded, non-cluttered objects that have their 3-D models in the system. Instead, the human vision gives us an understanding of the visual scene with ranges and distances.
Existing theories of perception give a very generic picture of possible information processing on the level of the entire brain, mapped to the particular cortical areas. Researchers have identified the major pathways of visual information in the brain that are related to different activities of the visual system. Instead of being a parallel process, vision appeared to be a multithreaded sequential process with two different but interconnected systems. Narrow foveal vision provides the separation of figure from ground, object identification, semantic analysis, and precise control of actions. Rough, wide peripheral vision identifies and tracks salient motion, guiding the foveal system to salient objects. It also provides the scene context.
Different phases of the vision process are known as low-, mid-, and high-level vision. Low-level vision is related to features and is very well studied. How the mid- and high-level vision works—has always been a mystery. Without methods that work with visual information as mid- and high level vision does it is not possible to create full-scale perception for robots and unmanned vehicles.